Each year in North America there are approximately 250,000 ACL injuries—about 70% of which are non-contact incidents. [Griffin LY. Noncontact Anterior Cruciate Ligament Injuries: Risk Factors and Prevention Strategies. [Journal of the American Academy of Orthopaedic Surgeons: 2000; 8:141-150] A near universally accepted and scientifically supported explanation for this non-contact statistic is the rotational and translational forces created when a player makes a sudden change in direction or stops. Exacerbating this natural force generation is athletic-shoe/playing-surface interfacetraction. Decades of private and academic studies prove a causal relationship between the increased desire for traction at the athletic-shoe/playing-surface interface and injurious forces that traction puts on the ACL. At some point, the human body is naturally unable to compensate for this force. Boden, Griffin and Garrett posit in their 2000 paper titled “Etiology and Prevention of Noncontact ACL Injury” the hormonal, anatomic and neuromuscular factors that may predispose athletes to ACL injuries. Regardless, athletic shoe manufacturers continue to produce shoes with ever more traction. Today, those shoes are being used on artificial turf, which is also designed to provide maximum traction.
Clearly, the conditions exist for even higher incidences of non-contact ACL injuries that sideline athletes of every age, gender and skill level. Yet few attempts at preventing non-contact ACL injuries have involved a viable athletic-shoe solution. Results have yielded shoe designs with unstable vertical profiles that compromise athletic performance and increase injury risk. U.S. Pat. No. 3,668,792 A (York) Jan. 8, 1971, entitled Breakaway Athletic Safety Shoe describes a breakaway system that, under duress, separates a spring-biased lower sole of the shoe from the upper section of the sole. U.S. Pat. No. 7,254,905-B2 (Dennison) Aug. 14, 2007, entitled Releasable Athletic Shoe Sole details a fully detachable lower sole with a mechanism designed to release when a pre-determined and specifically longitudinally directed force is applied. Published US Application 2013/0318832 A1 (Brown, et al) Dec. 5, 2013, entitled Self-Recovering Impact Absorbing Footwear, proposes an athletic shoe design which will allow the wearer of the shoe uninterrupted usage while dampening forces that surpass an injury threshold using a system of internal beams of various heights coupled with an internal air valve system. In spite of these, the incidence of non-contact ACL injuries continues to rise—painful proof that a practical solution has yet to be realized.